ZA200603818B

ZA200603818B - A wave power apparatus having a float and means for locking the float in a position above the ocean surface

Info

Publication number: ZA200603818B
Application number: ZA200603818A
Authority: ZA
Inventors: Resen Steenstrup Per; Hansen Keld; Arpe Hansen Niels
Original assignee: Wave Star Energy Aps
Priority date: 2003-10-14
Filing date: 2006-05-12
Publication date: 2007-11-28
Also published as: CY1113936T1; PT1682776E; AU2004282254A1; CN1878952A; WO2005038248A1; US20070102937A1; AU2004282254B2; DK1682776T3; BRPI0415344B1; NO333160B1; WO2005038247A1; CA2541432C; BRPI0415417B1; EP1678419A1; CA2541431A1; ZA200603815B; CN1878952B; AU2004282253B2; CA2541432A1; BRPI0415344A

Description

A WAVE POWER APPARATUS HAVING A FLOAT AND MEANS FOR LOCKING THE FLOAT IN A

POSITIO N ABOVE THE OCEAN SURFACE

Technican | field

The present invention relates to a wave power apparatus for converting power of sea or ocean waves Into useful energy, such as electricity. The appasratus according to the invention

Is specifi cally designed to withstand extreme sea wave conditions occurring during storms and hurricanes.

Backgrotund of the invention

Itis well known that sea waves appear to constitute a nearly unlimited resource of energy which, If exploited efficiently, may possibly solve a significant= proportion of the world’s energy problems. However, despite of many attempts to exp loit sea-wave energy, no commercially successful system for converting sea wave ener-gy into electrical power has been devised so far.

In general, three different types of wave power apparatuses mhave been proposed in the prior art. One such apparatus is disclosed in US 6,476,511, the apgparatus comprising a plurality of buoyant cylindrical body members connected together at thelr ends to form an articulated chain-like structure. Each pair of adjacent cylindrical members is connected to each other by a couplimmg member, which permits relative rotational movement of the cylindrical members about a transverse axis. Adjacent coupling members may permit relative rotation about mutually orthogonal transverse axes. Each coupling member Is provided with elements, such as a set «of hydraulic rams, which resist and extract power fromm the relative rotational moveme mit of the body members. The apparatus floats freely in the sea surface and is moored to the sea floor, .

A second type of wave power apparatus comprises one or mere surface floats capable of moving along the surface of the sea under the action of wave=s, and a reference member, which Is Fully submerged In the sea at a certain depth, and which is substantially unaffected by the waves, cf. for example US 4,453,894. The movement «of the float in the surface of the sea causes the displacement of a hydraulic fluid in a hydraulic system comprising hydraulic devices vwhich interconnect the surface float or floats and the reference member, whereby useful err ergy may be extracted from the hydraulic system. Ic will be appreciated that this apparatus is also moored to the sea floor.

Finally, a third type osf wave power apparatus is one having one or mo re arms supported by a supporting structure - carrying one or more floats which are caused to rmove by the waves. The energy of moving wa-ves transmitted into the arms and may be convewed into a hydraulic - system, as in the sys tem of US 4,013,382, or into a mechanical systerm of shafts which, via a mechanical transmisssjon system, drive one or more electric generatorss for the production of electricity, as in the ssystem of WO 01/92644.

The present Inventior is generally concerned with the third type of wa ve power apparatuses mentioned above. It has been found that one general problem in such systems is to prevent extreme impacts occaurring during storms and hurricanes from damagi ng the floats, arms and other parts of the wa ve power apparatuses. It is therefore an object o-f preferred embodiments of the gpresent Invention to provide a wave power apparatus, which is capable of withstanding extre=me sea wave conditions. It is a further object of preferred embodiments to provide a wave po’ wer apparatus which may conveniently be taken out of operation, e.g. to prevent formation of ice on various parts of the apparatus during operation. It is a still further object of pref~erred embodiments of the invention to provide arm apparatus, which allows for convenient= maintenance access to arms and floats, most preferably to allow for : maintenance access eof individual arms and floats In systems comprisirg a plurality of arms, each provided with a float.

Summary of the invention

The present Inventior accordingly provides a wave power apparatus ceomprising at least one arm, which is rotatabmly supported at one end by a shaft, and which caarries a float at its other end, which Is opposite to the supported end, so that a translational meovement of the float caused by a wave ressults in rotation of the arm around the shaft, the -apparatus comprising power conversion me=ans for converting power transmitted from the wave to the arms into electric power, the waave power apparatus being characterised by a hy~draulic lifting system for lifting the float oumt of the ocean and for locking the float in an uppeer position above the ocean surface.

Thanks to the hydraulic lifting system, the float may be withdrawn fro m the ocean and kept

In a locked position a_bove the ocean surface at the occurrence of e.g. storm or prior to the occurrence of icing. Thus, the only Impact on the float when It is withcdrawn from the ocean is the Impact of wind, the forces of which are significantly smaller than t-he forces of waves. In one embodiment, thes arms may be lifted out of the water by generatimg a hydraulic pressure in the hydraulic liftincg system, which causes the arms to be displaced out of the ocean, and by appropriately shutting a valve, preferably by means of a conical locking pin, so as to maintain the lifting pmressure. The hydraulic lifting system may be controlled from a remote on-shore location, or by a control system which formss part of the wave power machine, sand which ads in response to a signal indicative of a storrmy condition, e.g. to a signal from =n electronic device for continuously determining the vel ocity of wind. The control system nay be pro grammed to withdraw the float and arm from the water at a predetermined wave height . For example, this wave height may be a certa. in fraction, e.g. 30%, of the largest predicied wave referred to the operation site of the agpparatus, the so-called “100-year wave”_. At an ocean depth of 20 m, this height is appr—oximately 18 m, and the contro! sy~stem accordingly takes the float and arm out of the ocean at a wave height of approximately & m.

The wave height may be determined by a mechanical , optical, electro magnetic or acoustical systens, e.g. a pressure transducer system with a pre=ssure transducer arranged on the ssea floor, &n echo sound system arranged at the floats, a n echo sound system arranged on = fixed ssupporting structure of the apparatus and pointing upwards towards the surface of ~ the waves , or operating In alr pointing downwards towarcl the water surface, or a sensor sysstem with lleght transmitting or light receiving means arraneged on the floats and/or on the fixe=md suppomrting structure, such light being, e.g., laser ligh t. Alternatively, there may be provilided a radar ssystem at the structure. The pressure of a hydraulic medium in the lifting system mmay be gererated by a pump forming part of the hydrauliec lifting system. Alternatively, the pressLare may be generated by releasing pressurised hydraulic medium from an appropriate hydrawilic accumulator. The accumulator may e.g. be charged by a hydraulic driving system which, in one embodiment of the invention, is comprised in the power conversion meanss. For example, the accumulator for delivering the hydraulics lifting pressure may be an accumulator, or a plurality of accumulators in a so-caalied accumulator battery, for forcin gthe float Ito the wave at a wave trough as described In cdetail below.

In pre ferred embodiments, the apparatus comprises -a plurality of arms, each provided v=vith a float. 7In such embodiments, the hydraulic lifting systeem is preferably adapted to Individually lift each float out of the ocean. For example, the liftlimg system may comprise a plurality of hydrawmulic circuits, each of which Is associated with orme of the arms, and each of which comprises valve and/or pump means for pressurising the hydraulic circuit for lifting the &am and float out of the ocean. In one embodiment the hwydraulic lifting system comprises fewner pumpss than circuits, so that the or each pump is conmnected to a plurality of circuits, eac h circuit with associated valves being designated to In preferred embodiments off the invent=ion, the power conversion means and the armss are arranged such that those arms, which are kept in the ocean, may dellver power to th e power conversion means, while 0 ne or more sother arms are kept lifted out of the ocean. Embodiments incorporating the power— convewrsion means of WO 01/92644, which Is hereby incorporated by reference, may allow for free-wheeling, around a driving shaft of the power conversion means, of arms which are= lifted eout of the ocean. Embodiments relying on hydr.aulic power conversion means, in warhich movermnent of the arms generates pressure in a hydraulic driving system, may comprise p=] means for tak ing out of operation those power corversion means, e.g. those hydraaulic actuators, whilich are associated with an arm, whic h has been lifted out of the ocear. In a presently preferred embodiment, an arm may be Rifted out of the ocean and locked In an elevated posit=ion by the arm’s actuator, e.g. a dowuable-acting cylinder, which may b e used to lift and lock tte arm.

Preferred embodiments of the present invention a Iso provide a solution to the prob lem of providing a st able rotational support of the arm or— arms, which is less vulnerable t© horizontal forc=e components. It has been found thmat the structure of US 4,013,382 is likely to become unstamble due to horizontal force compone=nts generated by waves. More sp edfically, the bearings of the connecting rods are constitute d by simple pins, and any slight slack In such bearingss might cause Irreparable damage to the connecting rods and their support. The apparatus of BJS 4,013,382 Is therefare unsuitable= for Installation at the open sea, E.e. at relatively larg e wave forces. The structure disclose=d in WO 01/02644 also suffers from the disadvantage that even the slightest slack in the one-way bearings which support t=he rocker arms and whiech connect the rocker arm pipes andll the force shaft might damage th-e bearings. Mor—eover, the apparatus of WO 01/026=14, in which a total of some 40 ro-cker arms are supported by one single force shaft, requires &n immensely strong force shaft wvhich, due to its dimenslaons required in order for it to be able to transmit the required power, would be unfeasible due= to Its weight conferred by its farge dimensions, such large dimensioms being necessary due to the momentum transmitted frorw the arms to the force shaft. Preferred embodiments of the apparatus according to the pmresent invention provide an improved support of thez arms which makes the apparatus less vulnerable to horizontal force components. “Therefore, In a preferred embodiment, the apparatus of the Invention comprises a pair of pre-sstressed and essentially slack-free bearings. The bearings are thus cagpable of efficiently counnteracting radial and axial forces an=d consequently to withstand horizontal force components conferred by waves. The term w= slack-free bearing” should be unclerstoad to comprise any bearing, which is slack-free in a hor zontal and axial direction. For excample, the pair of bearings may comprise two conical bearings with their conical faces being opposite to each other. Irm one embodiment, the bearings are pressure-lubricated.

In another en—bodiment, the bearing comprises ar inner and an outer ring or cylinder, the inner ring belrg secured to a rotational shaft of thee arm, and the outer ring being ssecured to a fixed support, the bearing further comprising a #lexible material between the inner and the outer ring. Dum ring operation, the inner ring rotate=s relative to the outer ring, thereby twisting the flexible maaterial. In order to adjust the stiffness of the flexible material, there rnay be provided at leaast one cavity or perforation In the rmaterial. The flexible material ma-y, e.g., comprise a sp ring member, such as a flat spring. By appropriate positioning of the perforations) or by appropriate design of the spring member(s), the bearing support may be designed to- have a larger force-bearing capacity in one directi on than in another direction.

The arm is gpreferably supported by the bearings at two mountiing points which are offset from a centre axis of the arm, the centre axis of the bearings being coincident with an axis of 5 rotation of ®:he arms. As each arm Is connected to and support=ed by individual bearings, a stable rotational support for the arms is achieved, In particulasr, as the two bearings are preferably aarranged at a mutual distance along the axis of rotzation of the arm, an impact at the axis ressulting from a horizontal force component on the ficoat may be counteracted.

It will, accomrdingly, be appreciated that the structure of the pr—esent apparatus is more stable than the staructure of prior art devices. As the present apparat=us is primarily intended as an off-shore construction, stability Is a major concern due to costts of maintenance at off-shore sites. Maint=enance costs at off-shore sites are typically on ave=rage 10 times higher than maintenance costs at on-shore sites.

In the apparatus according to the invention, there is preferably provided a plurality of arms which are &arranged in a row such that a wave passing the rowav of arms causes the arms to successively pivot around the axis of rotation. The arms are preferably arranged at mutual : distances, =so that at all times at least two of the arms simult=aneously deliver a power contribute Tto the power conversion means. The power conversion means preferably comprise a hydraulic actuator assoclated with each arm, the hydraulic &actuators feeding a hydraulic medium into at least one hydraulic motor via shared hydrauliec conduits. Accordingly, an even power output of the power conversion means may be achleve=d. This is in particular the case in embodinments of the apparatus comprising a large number of arms, floats and actuators, e.g. 60, as the sum of the power contributes of the Individual actuators is essentially constant ower time. Possible pressure ripples on the pressure side of the hydraulic motor may be essentially eliminated by means of a spike suppression de>vice which is known per se, the spike suppression device being arranged in fiuld communication with the shared hydraulic conduits. Pereferably, the sum of all power contributes Is essemntlally constant at a certain } wave climaate, l.e. wave height and wave frequency. The hydr—aulic motor Is preferably a hydraulic rmnotor with variable displacement volume per revoli_ition. Changes In the wave climate mamy be compensated by means of a control circuit which controls the displacement volume pem revolution of the motor in order to keep the rpm «of the motor essentially constant. In order to generate alternating current at a glven tfrequency without utilizing a frequency «converter, the rpm of the motor should be controlleable within +/- 0,1-0,2%. In case a diffezrent type of hydraulic motor Is applied or in case the rpm is not controlled exactly, a frequency controller may be employed for fine-adjustment «of the frequency of the AC current gemnerated.

In preferred embodiments, the apparatus of the present Inwention comprises at least 5 amrms, such as at least= 20 arms, preferably at least 40 arms, prefezrably 50-80 arms, such as 555-65 arms, e.g. 60 a rms. The arms of the apparatus are preferably distributed, such that ther—e ls provided at least five arms, preferably at least 10 arms, per wavelength of the ocean waves.

Atthe open sea, the wave length of the ocean waves is typsically 50-300 m, such as 50-=200 m. In protectecl waters, the wave length of waves Is typicatily 5-50 m.

In preferred embodiments, the apparatus spans over at least two wave lengths. This brimngs about the posst bility to arrange a row of arms and floats at= a relatively large angle with respect to the wvave heading, e.g. at +/- 60°, as the wave Bength projected onto the orientation of the row of floats spans over at least 2 x cos( 60°) wavelengths, i.e. at leas one wavelength, whereby it is ensured that a power contribute Is delivered at all times.

The plurality of arms are preferably arranged in one or mo re rows, e.g. in a star, V or hexagon formation as disclosed in WO 01/92644. In order to efficiently exploit the wave: energy, the rowv of arms Is preferably oriented such with re=spect to the wave heading th at the row forms an a ngle of within +/- 60° with respect to the waave heading.

It has been found that the efficiency of the apparatus acco rding to the invention increas es with increasing buoyancy of the float with regard to its dry— welght. Accordingly, in prefe-rred embodiments Of the invention, the buoyancy of the float Is= at least 10 times Its dry welcaht, such as at least 20, 30 or 50 times, preferably 20-40 timess. For example, the dry weigh tof a float is typically 100 kg or less pr. meter cube of buoyancy=, the buoyancy of salt water boeing : typically appro>imately 1050 kg/m>. A float is typically ma de from hard low weight foan— materials or balsa wood, which are coated with a composit=e, such as reinforced glass fitoer composites or @ combination of glass fiber and carbon fibe r composites. Alternatively, a float may be made From a sandwich layer of reinforced fiber mamteriel with hard foam being provided in thee middle of the sandwich and at the bottorn =and at the top of the float, witkh the foam layers be ing separated by a honeycomb structure of reinforced fiber materials.

Efficiency also increases with Increasing diameter of the float relative to its height. Prefearably, the diameter of the float is at least 5 times Its helght, such as at least 7 times, such as zat least 10 times, or 5-20 times. In preferred embodiments, —the float has an essentially cir—cular cross-section, @nd in order to Improve fluid dynamical progperties of the fioat, it may hawe a rounded edge portion, which acts as a streamlining. ’

The power conversion means preferably comprise a hydramulic driving system with a hydraulically dwiven motor. For example, each arm may be connected to the hydraulic d™ riving system by meaans of at least one actuator which causes a Bhydraulic medium of the hydraaulic

We’ O 2005/038248 PCT/DK2004/00070S drivving system to be displaced into a hydraulic motor, the actuator(s) being arranged to displace the hydraulic medium to the motor via hydraulic conduits. In case of several arms anc several actuators, the hydraulic medium Is preferably displaced to the motor via shared hyciraulic conduits. In other words, several hydraulic actui ators may feed hydraulic medium into one single hydraulic motor via a shared system of hydraulic conduits. Most preferably, the hydraulic medium is not accumulated in a hydraulic s®orage tank for accumulating hyciraulic medium under pressure, from which pressure iss released to the motor. Accordinglwy, the actuators feed hydraulic medium directly Into the hydraulic motor. However, as discusse=d belcow, a battery of hydraulic accumulators may advantagseously be applied for an entirely different purpose, i.e. for forcing a float into a wave near a wave trough. As in preferred emibodiments, a plurality of actuators simultaneously trarismit power to the motor, there is no =need for a hydraulic storage tank, as the motor will be= capable of running at a subsstantially constant speed and at a substantially consteant power input thanks to the del@ivery of power In the shared hydraulic system from a plurality of actuators at a time.

It s=hould be understood that there may be foreseen more than one single hydraulic motor.

Preferably, two, three or more motors may be arranged imn parallel at the end of the shared hydraulic conduit. Thus, the power delivered through the shared hydraulic conduit may drive several motors. If, for example the hydraulic driving systeem produces 4 MW, eight motors delivering 500 kW each may be coupled In parallel at the shared hydraulic conduit. The motors may deliver the same nominal power output, or tHhey may deliver different nominal pov=ver outputs. For example, one motor may deliver 400 kW, one may deliver 500 kW, etc.

All _hydraulic motors may also be linked through the same through-going shaft, which drives: at |. east one common electric generator, or all hydraulic nmotors may drive one cog wheel which drives at least one common electric generator

In order to allow the hydraulic system to force the arm(s2) and float(s) in any desired direzction, each actuator may comprise a double-acting cy~tinder which may be used to extract ene=rgy from the arm into the hydraulic system and to feed energy from the hydraulic systerm

Into the arm, e.g. to drive the float into a wave near a waave trough as explained in detail below in connection with the hydraulic accumulators, The= hydraulic lifting system preferably corenprises one or more pumps for pumping hydraulic mectium into the cylinders for lifting theam out of the ocean.

In preferred embodiments, the apparatus comprises mea ns for forcing the float(s) into the wales at wave troughs, so as to increase the vertical distzance traveled by the float to increase the power output in a wave cycle, Such means nenay e.g. comprise one or more hydraulic accumulators for intermittently storing energy iw the hydraulic driving system. The= energy stored in the hydraulic accumulators may advantageously be derived from the release of potential energy as the float Is taken out of the water a wave c=rest. In other words, as a float moves from a submeerged position In a wave near a wave cre=st to a position above water, potential energy iss released. This energy may be accumulated in the accumulator or in a battery of accumulatorss, wherein different accumulators are charged at different pressures, e.g. at pressure steps according to the number of accumulators. Tn embodiments incorporating such hydrasulic accumulators, the hydraulic driving system may be controllable to release the energy sto red in the accumulator(s), when a float #is passed by a wave trough, so as to drive the float carried by the arm into the wave. To impreove the efficiency of the accumulator system, these may be employed a plurality of accunulators, such as at least 2, such as 3-20, such as typically 6-12, which preferably store hydraaulic medium at different pressure steps. In prefermed embodiments, the float is driven a certain distance into the wave near a wave trough, and subsequently the float is allowed to mo\vve upwardly in the wave, but yet submerged in the wa ve, and at the wave crest the float Is rel=eased, i.e. allowed to move out of the water. As described above, the energy released as the float Is released at the wave crest is used to charge tine one or more hydraulic accumulators, aat which energy is stored for driving the float into the wave. Accordingly, the potential energy released as the float moves out of the wave near the wave crest is not lost. On the contrary, Itis utilized for driving the float into the wave at the wave trough, whereby the total vertica 1 distance traveled by the float Is increased. Consecjuently, the power output of a wave cycle Is increased. It is estimated that, at a wavee height of 1.5 m, the vertical distance t:raveled by the float may be increased from approximmately 0.75 m to approximately 1.5 m, tinus doubling the power output. The energy utiliz ed to drive the float into the wave at the wave trough causes essentially no loss in the driving system, as the energy Is provide=d by the release of the float at the wave crest.

In order to allow for accurate control of the system, each cylinde=r, or at least selected ones of the cylinders, may be provided with a sensor for determining a position and/or rate of movement of the cylinde=r’s piston, the sensor belng arranged to transmit a signal to a control unit of the cylinders and associated valves, so that the transmisssion of energy from the

Individual cylinders to th-e remaining parts of the hydraulic drivin g system is individually controllable in response ®o the signal representing the individual cylinder’s piston’s position and/or rate of movement. Thus, the cylinders may be individuall=y controllable, and a cylinder may be withdrawn from operation, e.g. for maintenance, while tke remaining cylinders keep operating, so that the ermtire system will be essentially unaffectec by the withdrawal of a single cylinder. The sensor is preferably also utilized to control time depressing of the float into the water, i.e. to control release of pressure of the battery of accumulators as described above. The sensor may f=urther be utilized to control charging of - the accumulators, i.e. to determine the passage cf a wave crest. Moreover, the sensor is museful to control releasing of the flcoat at a wave crest, i.e. to prevent a catapult-like= shoot-out of the float=. The sensor may also be used for monitoring the power output of e=ach individual actuato r in the hydraulic drivineg system, so that the power output of the indiviclual actuators and the entire apparatus as succh may be optimized.

Where=as some prior art systems rely on submerged reaference members for ssupporting those meanss which convert sea wave power into useful power or on shore-supportss, It has been found that wave energy Is most efficlently exploited or the open sea. Accord ingly, the apparatus of the invention preferably comprises a supporting structure whict Is fixed to the sea floor. In a presently preferred embodiment, the stzapporting structure is flixed to the sea floor boy means of a suction anchor, or alternatively by— a gravity foundation, »or fixed to a rocky seabed with studs. The supporting structure ma=y advantageously comprise a truss structrure, with the suction anchor being arranged at a first nodal point of the structure. At least cone arm and preferably all arms of the apparatuss are supported at seccond nodal points of the truss structure, most preferably at a summit of a triangular substructL are of the truss struct ure. The triangular substructure may define two vertices at the sea flocor, with a means for att=aching the structure to the sea floor in each of t he comers. Preferably ,.. the means for attactming are at least partially embedded in the sea floor, e.g. under by gravity foundation or a suct=lon anchor. As the means for attaching are arrarged at the nodal point=s of the truss structrure, vertical forces in the truss structure caused by the buoyancy of thee floats may efficle .ntly be counteracted. A truss structure as described above ensures a maximum degree of stalbllity of the system while allowing for a low overaall weight of the supposrting structure.

Brief cescription of the drawings

Prefer—red embodiments of the invention will now be fuxrther described with reference to the drawimngs, in which: '

Figs. =1 and 2 are cross-sectional illustrations of an em : bodiment of a wave pcower apparatus accorcding to the invention;

Figs. =3-5 show three embodiments of a truss structure= of an embodiment of the wave power appar-atus according to the present invention;

Fig. 6 lllustrates a honeycomb structure of a float;

Fig. 7 lliustrates a supporting structure for an arm of t=he apparatus of Figs. XL and 2;

Figs. 3-13 show various bearing assemblies for an arr of the apparatus;

Fig. 14-17 show diagrams of a hydraulic driving system of an embodiment of &n apparatus according to the invention;

Fig. 18 shows a diagram of a hwydraulic lifting system for lifting the floats out oef the ocean;

Fig. 19 Illustrates a wave powemr apparatus with an array of floats extending accross two wave crests;

Fig. 20 shows hydraulic pressure as a function of time in a feed line of the hydraulic driving system of a prior art wave poweer apparatus and in an embodiment of an appa ratus according to the present invention, respectively;

Fig. 21 illustrates two different travel paths of a float across a wave, Flg. 22 shows a diagram of a hydraulic driving system with accumulators for forcing the floats into the waves at wave troughs ;

Fig. 23 illustrates the stepwise accumulation of energy in a hydraulic storage ssystem; : Figs. 24 and 25 are diagrammatic illustrations of the movement of waves and - floats.

Detalled description of the drawsings

Figs. 1 and 2 show a cross-sect ion of wave power apparatus 102 comprising a truss structure 104 which may e.g. be of a so-ecalled space truss structure. The truss structures, which Is also illustrated in Figs. 3-5, comprise=s an essentially triangular lower part with first:, second and third force members 106,108,1 10, and an essentially rectangular upper part 1 11, As illustrated in Figs. 3-5, the rectangular upper part extends a distance perpendicular to the plane of Figs. 1 and 2, whereas there Is provided a plurality of distinct lower triangular lower parts. The rectangular upper pasrt may be used for accommodating hydraullc a nd electric equipment, including the hydrawlic driving and lifting system, and it may furtheer be used as a as catwalk or footbridge for maIntenance personnel. The truss structure define=s first, second, third, fourth, fifth and sixth nodlial points 112,114,116,117,118 and 120. Prefemrably, the force members are essentially rigid, sso that they may withstand tension and compre=ssion. The first and second nodal points 112,11 4 are provided at the sea floor and are retaineed at the sea floor by means of, e.g., suction anchors 121 indicated in Figs. 3-5. Alternatively the first and second nodal points 112,114 m.ay be supported by a concrete foundation at th e sea floor.

Arms 122 carrying floats 124 are rotationally supported at or near the third anad fourth nodal points 116, 117. Figs . 3-5 show a perspective view of the truuss structure for supporting a plurality of arms on e=ither side of the structure. It should be= understood that the truss structure of Figs. 3-5 may have a wider extent than actuaily~ depicted in Figs. 3-5, so that IE comprises e.g. twent=y or thirty triangular sections, whereby an arm may extend away from the truss structure at= each of the nodal points 116,117. A pt urality of truss structures as those of Figs. 3-5, sumch as three, six or more truss structurexs, may be arranged in a star, \W'- or hexagonal arrangement in order to Increase the number cof arms and floats Included in amn installation comprising the apparatus of the invention or a p lurality of apparatuses accordin- © to the invention.

The third, fourth, fiftEh and sixth nodal points 116,117, 118,7120 are provided above the surface of the sea at a height sufficient to ensure that they are also above the sea surface when waves are highm under stormy conditions. For example_, the nodal points 116, 117, 1183 and 120 may be prowrided at 20 meters above the surface of the sea when the sea is smoot=h.

In order to transforma the energy of the waves into hydraulic energy, the wave power apparatus 102 compt—ises a plurality of arms 122, each of which at one end comprises a flo=at 124 and at the oppossite end is connected to a shaft 126. Th e arms are adapted to rotate around the shafts 12«6. Each arm 122 Is attached to a hydra ulic actuator, such as a hydraul ic cylinder 128 comprising a piston 130. The hydraulic cylinde=r 128 is pivotally connected to the arm in a first attachment polnt 132 and to the truss striacture 104 in a second attachment point 134. The secon d attachment point is preferably locatead at a nodal point, i.e. along an edge portion of an esssentially rectangular structure arranges on top of the triangular main structure of the trusss structure. The floats 124 move the arr ms up- and downwardly influenced by the mo vement of the waves. When the arms rove upwardly and downwardly, the piston 130 is mowed, and thus the wave energy is transformed into hydraulic energy which may be converted into useful electric energy as described below in connection with

Figs. 14-18 and 22.

As shown In Fig. 2 thee hydraulic cylinders 128 are adapted t=o lock the arms 122 in an elevated position whearein waves can not reach the arms 1222 and floats 124, the arms beingg drawn to their elevateed positions by the cylinders 128, It is ®&hereby possible to protect the arms 122 and floats =124 during a storm or when ambient te-mperatures near or below the freezing point of the water of the ocean Hsk to cause formatzion of ice on the floats. The hydraulic cylinders 1-28 are connected to a hydraulic lifting ssystem for locking the hydraulic cylinder in the elevateed position, the hydraulic lifting systenm belng discussed in further detaall in connection with Fics. 18 below. The floats 124 may be pivotally connected to the arms 12 2,

Accordingly, when thee arms are elevated during a storm, the= floats may be rotated to a position wherein theyw are essentially parallel to the wind direzction. Thereby, the surface which the wind acts on is limited and thus the force acting o-n the floats 124 Is reduced and the torque transferred to the truss structure 104 via the arms 122 is reduced. Furth ermore the floats are designed with an aerodynamic shape with rounded edges (not shown)s, so as to reduce the wind forces on the apparatus.

As shown in Figs. 3-5, the truss structure 10-4 may include diagonal force members 113, 115 (rot shown In Figs. 1 and 2) for providing a further support at the nodal points 116, 117,

In Figs. 4 and 5, the truss structure Is loadedll with a weight acting downwardly to re :duce the upwards forces at the anchors 121. The welg ht Is brought about by a longitudinally eextending weight, such as a water tank 123 (Fig. 4), or by a plurality of distinct weights, such as water tanks 125 (Fig. 5).

Fig. 6 shows a structure of an essentially holBow float 124 comprising a honeycomb sstructure 127, which supports the outer walls of the fioat.

Fig. 7 shows one of the arms 122 which Is pivotally attached to a float 124 and Is adllapted to rotate around a shaft 126. The arm Is connected to the shaft at first and second attachment } points 136, 138 which are offset from the certre axis 140 of the arm. The shaft 126 is rotatably supported by a fixed support structmure 142 comprising two bearings 144 amrranged to counteract radial and axlal forces.

In order to provide an essentially maintenance-free bearing support for the rotation of the arms 122, the present inventors have propos ed bearings as those shown in Figs. 8-M.3. The bearings of Fig. 8-13 may be incorporated as a bearing 144 in the bearing structure lllustrated In Fig. 7 and are particularly well s uited for supporting an shaft, the rotati- onal amplitude of which is 30 degrees or less durirag normal operation, l.e. £15 degrees or less, such as 20 degrees or less, i.e. 2:10 degrees or less. When the arm is to be pivoted ®&o the secured position of Fig. 2, the fixing of the outer ring 147 may be loosened, so that =a larger rotational amplitude Is allowed, e.g. +40 deggrees. Traditional roller or ball bearings have a !5 short life time at such small rotational amplitudes, as their lubrication medium usualzdy only fulfils its purpose to the desired extent at continuous rotation at a higher rotational s=peed than the one conferred by the arms 122. The bearing of Fig. 8 Includes an Inner ring or cylinder 145 and an outer ring or cylinder 147, between which there Is provided a fle=xIble substance 149, e.g. a rubber material. The inmner ring 145 Is secured to the rotating sshaft, ‘0 and the outer ring 147 Is secured to the staticonary support of the shaft. Thanks to thme elasticity of the flexible substance 149, the inmner ring may rotate relative to the oute rring, so as to allow the supported shaft to rotate with respect to its support. As the outer rincy 147 is supported by or fitted Into a fixed structure, e=.g. squeeze fitted along its outer periptery, there is provided an axial and a radial support= of the shaft. The stiffness of the flexib le substance 14%) may be adjusted by providing cavities 151 _ such as bores or perforations, Bn the material. “The maximum load supportable by the bearl ng may be Increased by increas®ing the length of the bearing (i.e. transverse to the plane of Fig. 8). The number and dimensisons of the cavitiess 151 may be selected to fit a particular purpose, e.g. to minimise notch sensitivity or to maximise the axial force to be counteracted by the bearing. A like bearing 344 is shown in Fig. 9, which has fewer cavities 151 to inccrease the force-bearing capacit=y of the bearing ir one direction.

Similar wrigg le bearings 346, 348 and 354 are shown in Figs. 10, 11 and 12, respectively -.

These bearinegs comprise inner and outer rings 145, 147 with one or more flat springs bel ng interposed bextween the rings. In Fig. 10, there Is provideed two flat springs 147, each of which forms he shape of the number 3. The arrows 345 and 347 indicate that the force- bearing capascity Is larger In the vertical direction (arrows 345) than In the horizontal direction (arrows 347). In the bearing 348 of Fig. 11, the re Is provided one flat spring element 352, which defines a plurality of cavities 353. Arsows 349 and 350 indicate that Whe force-bearingg capacity of the bearing Is larger in the vertF cal and horizontal directions tha nin non-horizontal and non-vertical directions (arrows 350). @Bearing 354 of Fig. 12 comprises two H-shapecd flat spring elements 362, each defining an outer and an inner portion 364 =and 366 as well aas an interconnection portion 368. The stiffnexss of the bearing may be choser by adequate selection of the geometry of the spring elementcs 362. For example, the interconnecti ng portion 368 may be formed as an S. Arrows 355 and 357 Indicate that th-e force-bearing capacity Is larger in the vertical direction ttman in the horizontal direction.

The inner anad outer rings 145, 147 of Figs. 8-12 may be made from steel or from carbon fibre materia ts. The flat springs 342, 352 and 362 may lil<ewise be made from steel or ca rbon fibre materia Is.

The bearing gprinciples of Figs. 8-12 may also be used for providing a support for the hydraulic cylinders 128.

Fig. 13 shows=s a bearing support for an arm 122, the support comprising two flat springs 372 and 374. The first flat spring 372 increases the torsion stiffness as well as the transverse stiffness of the bearing. The flat springs may be made from carbon fibre materials.

In the hydratilic diagram of Fig. 14, there Is shown a plurality of cylinders 128 with respe=ctive pistons 130 wvhich are upwardly and downwardly movable= as the arms 122 and floats 12=4 move In the =waves, cf. the above description of Fig. 1. W™hereas there are shown three cylinders in t=he diagram of Fig. 14, It should be understood that the apparatus according to the inventiorm typically comprises a larger number of cylirmders, e.g. 60 cylinders. The cylinders 128 are shown as double-acting cylinders connected at thelr upper ends ~to feeding conduits 176 for a hydraulic medium of the system. In each feeding conduit 176 tere is provided a pressure valve 178. The feeding condultss 176 merge into a common m ain conduit 180, which feeds into a hydraulic motor 182 with vamriable volume displacement pe=r revolution. In the feeding conduits 176 and commor main conduit 180, there is maintained an operating pressure po. The pressure p, may advantageously also be the thresheold pressure of valve 178, at which the valve switches EDetween Its open and closed state. The hydraulic motor drives an electric generator 184, amd at the exit of the hydraulic rotor, the hydraulic medium is led to a reservoir 186. From th_e reservoir 186, the hydraulic medium flows back to the cylinders 128 via a common return conduit 188 and branch retuarn conduits 190.

In each of the cylinders 128, the piston 130 dividess the cylinder in upper and lower chambers 192, 194 which are interconnected via conduits 196 and 198. In each of the conduits 196 there Is provided a two-way valve 200, and in parallel thereto there is provided, ln conduit 198, a pressure valve 202 and a series flow controll valve 204. Finally, each cylineder is provided with a control element 206 for determinirmg the position and/or rate of nmnovement of the piston 130 of the cylinder 128. , When the two-way valve 200 is open, the piston 1-30 may move freely when the arms 122 (see Fig. 1) move in the waves. When the control element 206 determines a cert=ain position and/or rate of movement of the piston 130, a control signal Is passed to the valwe 200 causing the valve 200 to shut. As the pressure val-ve 178 Is shut, the piston 130 will be locked while the wave continues to rise until the bsuoyancy of the float is large erough to overcome the operating pressure pp In the feeding and main conduits 176,180, sso as to open the pressure valve 178. It will thus be understood that the float 124 (see Fig. 1) Is at least partially submerged in the wave when the valve 1778 opens (cf. also the below discussion of

Fig. 21). Once the pressure valve 178 has opened , the hydraulic medium is fed Wo the motor 182. When the float passes the wave crest, the float Is still submerged, but the pressure in the upper part 192 of the cylinder 128 drops, and pressure valve 178 shuts. Sutosequently, the two-way valve 200 opens, and hydraulic medEum is displaced from the lower cylinder part 194 to the upper cylinder part 192, as the float mmoves down the wave from the wave crest to the wave trough.

It will be appreciated that, due to the large numb er of cylinders 128, It Is at all ¥times ensured that at least two of them, and preferably several, deliver a flow of hydraulic me dium to the motor 182. Thereby, an even power output from the generator 184 may be enssured, preferably without any need for frequency converters.

The above description of Fig. 14 also a pplies to the Fig. 15, however in the embodi ment of

Fig. 15 there is provided a plurality of Thydraulic motors 182,208,210 are provided. Each of the hydraulic motors 182,208,210 is cednnected to respective electric generators 184,212,214, In the embodiment of Fig. 15, only three hydraulic motors and electric generators are provided, but In other eémbodiments the wave power apparatus comprises a higher number of motors and generators. For example 5, 10 or 20 motors and generators may be provided. The capacity of the Fydraulic motors and their corresponding ele=ctric generators may be chosen so as to make it possible generate different levels of en ergy. In one example, the three generators maay be able to produce 0.5 MW, 0.5 MW and 2 MW, respectively. Thus, In order to produce 1 MW, the hydraulic motor of the two 0.5 Mw generators may be connected to the ceommon main conduit 180, whereas the third generator should be disconnected from the main conduit 180. At sites where the wave energy is substantially constant over time, the capacity of the generators and their correspo nding hydraulic motors may each be chosen to be at the highest possible level in order teo reduce the total number of hydraulic motors &nd generators. At sites at high fluctuation otf the wave height and wave frequency, the capac ity of the generators may be chosen from a binary principle e.g. 1 MW, 2 MW and 4 MW. By choosing the generators from a binary pr—inciple it is possible to couple said generators in amnd out in using the below pattern so as optimise the utilisation of the wave energy.

Generator 1 Generator 2 Generator 3 Total output [MW] ome | awn | ams on | ok err ox | on orf 0002

I I A

I A I I on ow | ofS — oo | om fon | 0¢

The system of Fig. 16 Is similar to the system of Fig. 15, however In the system off Fig. 16 there is only provided one single electric generator 184, which Is driven by the hyedraulic motors 182, 208 and 210 via a gearbox 185. The hydraulic motors may e.g. drive a toothed rim of a planet gear. Alternatively, as shown In Fig, 17, the hydraulic motors 182, 208 and 210 may drive one common generatom 184 via a common, through-going shaft 18-7.

Fig. 18 illustrates a hydraulic lifting sywstem for lifting the floats 124 out of the ocesan and for keeping them in an elevated position, in which the waves cannot reach the floats. Fig. 18 also includes a hydraulic driving system similar to the driving system de=scribed above in connection with Figs. 14-17 . To the extent that the same or similar- elements are incorporated in the driving system depicted in Fig. 18 as those depicted in Figs. 14-17, the reference numerals of Fig. €5 are used In Fig. 8, and reference is made to the above description of Figs. 14-17 for a description of such elements and the eir functionality. The hydraulic lifting system of Fig. 18 is adapted to individually lift one or more floats 124 out of the water and to decouple the cylinders of the lifted floats from hyciraulic driving system. The system of Fig. 18 includes, in addition to the common return conduit 188, a conduit 266 connecting the reservoir 18 6 to a pump 268 driven by a motor 2703. Condult 272 connects the downstream side of the pump 268 to a number of one-way val-ves 274, the number of one-way valves being equa to the number of floats and cylinders M28. Condults 276 connect respective downstream sides of the vaives 274 to respective two-vway valves 278 and one- way valves 280, downstrea m of which the conduits 276 merge Into one common conduit 282.

The conduits 276 communiecate with the lower cylinder chambers 1.94 and conduits 198 via conduits 284. Further, the aconduits 276 communicate with the upper cylinder chambers 192 and feeding conduits 176 v ia the conduits 196. Finally, two-way valves 286 are provided in the branch return pipes 196), and two-way valves 288 are provided in conduits 198.

When an arm is to be lifted out of the water, valve 278, valve 286 and valve 288 shut. Valve 274 and 280 open, and the= pump 268 may force hydraulic mediurmn Into the lower cylinder chamber 194, and the arm associated to the cylinder in question i=s elevated. Hydraulic medium in the upper cylincler chamber 192 is conducted to the reservoir 186 via valve 280.

The control element 206 detects that the arm and with It the piston 130 has reached its desired position, e.g. its uppermost position, and a signal is passed to valves 274 and 280 causing them to shut. The piston 130 is consequently locked, and the arm is secured in a position, in which the float 124 is lifted out of the water. The arm 122 may be further supported by a pawl (not sshown) engaging the arm.

Fig. 19 is a diagrammatic i Hustratlon showing a plurality of floats 71.24 and 164 which are coupled to a hydraulic driving system via cylinders as described akoove in connection with

Figs. 14-18. In Fig. 19, those floats which are located at wave cressts 146,148 are referred to by reference numeral 164, whereas all other floats are referred to- by reference numeral 124.

There is, however, no struectural difference between the floats 1248 and the floats 164. First, second and third wave cressts 146,148,150 are indicated by double lines In Fig. 19, and first and second wave troughs 152,154 are indicated by single lines in the figure. The direction of movement of the wave fro nts is indicated by a first arrow 156, the2 wave length being

Indicated by a second arrow 158 and the rising and falling parts of the waves are Indicated by third and fourth arrows 16 0,162, respectively. As Indicated In Fig. 19, those floats 164, which are at the wave crests 146 and 148 have thus just completed ther upwards movement caused by the waves. Those floats 124 which are between the first vevave crest 146 and the first wave trough 7152 are on their way upward in the wave, whereass those floats which are between the secord wave crest 148 and the first wave trough 152 asre moving down along a downstream side ®of the wave. As the array of floats 124, 164 spans over a full wave length, a 5S plurality of floats fis on their way upwards in a wave at any moment,~ whereby it is ensured that a plurality of floats deliver a power contribute to the hydraulic driving system at any time. As describec above with reference to Figs. 14-17, each of the floats actuates a hydraulic cylinder » and hydraulic pressure Is created in the main cormduit 180 (cf. Figs. 14- 17). As a plurality— of the floats are moving upwards at the same timae, a plurality of hydraulic cylinders provide Bhydraulic pressure simultaneously. Accordingly, th anks to the provision of the common mairm condult 180 connected to a plurality of cylinders with respective floats and thanks to the extent of the array of floats over at least a full wave le=ngth, the pressure fluctuations In the= common main conduit 180 and thus the pressure= fluctuations at the input to the hydraulic nmotor 182 or motors 182, 208, 210 may be kept low. As the hydraulic motors 182, 208 sand 210 are motors with variable displacement pes turn, the rpm of the motors may be ke=pt essentially constant. This in turn confers the ef<fect that the frequency of

AC current generated by the generator 184 or generators 184, 212 and 214 is essentially constant, wherebwy it is achleved that, in preferred embodiments of “the invention, AC current may be generated without the need for frequency converters.

In Fig. 19, the wamve direction defines an angle 8 with respect to the= row of floats. The wave direction is paralle=! to the row of floats when 8 = 0°. It will be under—stood that the larger the angle 0 is to 0° th e longer must be the row of floats in order to ensLre that at any given moment at least eone float Is moved upwards by a wave to deliver a pressure contribute in the common main comnduit 180 (cf. Figs. 14-17) of the hydraulic driving system.

In designing the ssystem the typical wave length and directions of tie location should be taken Into account In order to ensure a substantially constant hydreaulic pressure in the system. In prefer—red embodiments of the invention, the relationshif> between the wave direction (angle 6-) and the length of the wave power apparatus, i.e— the length spanned by the floats 124, 164, may be determined by the following formula:

Lenght of thewawe power apparatus 2 wavelength cos(8)

Fig. 20 shows the= hydraulic pressure 242 In the common main conclult 180 (cf. Figs. 14-17) as a function of tlme 240. The first curve 244 shows the hydraulic poressure In a feed line of a typical prior art wave power apparatus with hydraulic cylinders feecling one accumulator with wWV0 2005/038248 PCT/DK2004/000705 a hydraulic motor. As indicated in Fig. 20, the hydraulic pressure fluctilates with a wave pe=riod 246. The hydraulic pressure 2248 In an embodiment of the wave power apparatus of thee present Invention comprising a plurality of arms, floats and cylinde=rs and no ac=cumulators fluctuates with a lower= amplitude.

Figg. 21 lllustrates two different trave=l paths of a float across a wave whhich moves in the dimectlon of arrow 171. The upper part of Fig. 21 illustrates a flow pati, at which no m easures are taken to increase the =vertical travel distance the float 1224 when the float is passed by a wave. The lower part of Fig. 21 Illustrates a flow path, at “which the vertical traavel distance of the float Is increased by actively forcing the float 12=4 Into the water at the waave trough 152.

Irm the upper part of Fig. 21, at positzion 1723, the float 124 is moving downwards with the w-ave until the float reaches the wave trough 152 at position 172b. At this point the hydraulic cylinder Is locked as pressure valve 178 shuts (cf. Figs. 14-17), two-wray valve 200 being also shut, and accordingly the float moves horizontally into the wave to po sition 172d via position 1772c. As the wave rises, pressure bauilds up In the upper chamber 1922 of the cylinder 128 ard in the conduit upstream of the poressure valve 178 (cf. 14-17). At position 172d, the pm-essure Is sufficient to overcome tine threshold pressure of pressure wyalve 178, which opens, w-hereby the float 124 is allowed to move upwards in the wave to position 172f via position 1=72e. During this movement, the hydraulic cylinder 128 of the float 1224 feeds hydraulic rmaedium Into the common hydraulic conduit 180, whereby a power comntribute is delivered to the hydraulic motor 182 or motors 182, 208, 210. At position 172f, w hen the passing wave is about to descend, the pressure in the feeding condult 176 drops belowv the shut-off threshold ofF pressure valve 178, which shuts. As soon as the pressure valve 1788 shuts and two-way vaalve 200 opens, the float 124 is uracoupled from the common hydraumlic conduit 180 and the buoyancy of the float 124 causes it tec move essentially vertically out eof the water to position 1~72g. As the wave descends, the ficoat 124 moves downwards with thee wave to position 1~72h, and the float starts a new cycle in the next wave. The float 124+ travels a vertical distance 168. From the above description of Fig. 21, it will be apprecisated that the power ceontribute of each Individual float 124 and associated cylinder 128 to the hydraulic driving swystem is conferred during the vertlical movement of float.

Ir order to increase the power outpsut of the wave power apparatus Itz is thus desirable to ircrease the vertical travel distances of the float 124. The lower part of Fig. 21 illustrates an a Rernative travel path of the float 1_24 across the wave, in which meaasures are taken to ircrease the vertical distance travel led by the float 124. At position 1774a, the float 124 is d escending at the downstream side of a wave. At position 174b, the f=loat 124 has reached the wave trough 152. At this point, the float is forced downwards under the water to position

174c, and pressure valve 178 a nd two-way valve 200 shut (cf. Figs. 14-17) . As the pressure upstream of the pressure valve 178 exceeds the threshold shut-off pressure of the pressure valve 178, the valve 178 opens , and the float 124 moves to position 174g \wia 174d, 174e and 174f. At position 174f, presssure valve 178 shuts and two-way valve 2022 opens, and the buoyancy of the float 124 cause=s the float to move essentially vertically out of the water to position 174h, from which the Float descends on the downstream side of the= wave to position 174i, and the above cycle is repeated. Thanks to the forcing Into the water of the float at the wave crest 152, i.e. from positi on 174b to position 174c, the vertical distan ce 170 travelled by the float is significantly larger than the vertical distance 168 travelled in embodiments, in which the float is not forced do=wn Into the wave at or near a wave trough, «cf. the upper part of Fig. 21. Thus, the power conatribute of the cylinder 128 of a float 124 is axalso significantly larger in respect of the path of the lower part of Fig. 21 than in respect of t—he path of the upper part of Fig. 21.

Evidently, a net gain in terms of overall power output of the wave power apoparatus arises only if the power utilized for forrcing the float 124 Into the wave at the wave= trough 152 is not deducted from the power output of the apparatus. Fig. 22 shows a modifiead embodiment of the hydraulic driving system of Fig. 14, which may accumulate potential ernergy released as a float 124 moves vertically out =of a wave at or near a wave crest, i.e. from position 174g to position 174h in the lower parts of Fig. 21. This energy, which Is lost in the embodiments of

Figs. 14-17, Is used to force thme float 124 into the wave.

More specifically, Fig. 22 show_s a hydraulic diagram with first, second, thir—d and fourth accumulators 216, 218,220,22=2 for forcing the floats down under the wave=s at wave troughs.

In addition to the system of Fiag. 14, the hydraulic system of Fig. 22 comprises the hydraulic accumulators 216,218,220,22=2, which are arranged at one end of hydraulic accumulator conduits 224,226,228,230, whaich are connected to the feeding conduits 1276 via first, second, third and fourth two-way valveas 232,234,236,238. Once a float has passec a wave crest, the pressure valve 178 shuts as deescribed above in connection with Fig. 14, ard the float 124 moves out of the wave from it-s submerged position in the wave. The hydraulic medium, which is thereby displaced frorn the upper part 192 of the cylinder, Is conducted to the accumulators 216,218,220,22:2 via the valves 232,234,236,238 and the aaccumulator conduits 224,226,228,230. In one embodiment, the valves 232,234,236,2=38 are arranged and controlled such that the fi rst valve 232 shuts at a first pressure pi, pL being lower than the operating pressure p0 in tlhe main conduit 180. The second valve 234— opens at the first pressure pl and shuts again amt a lower, second pressure p2. The third val=ve 236 opens at the second pressure p2 and shuts again at a lower, third pressure p3. The fourth valve 238 opens at the third pressure p=3 and shuts again at a lower, fourth pressure= p4. At a yet lower pressure p5, the two-way vale 200 opens.

At a wave trough, thme valve 200 shuts, the fourth two- way valve 238 opens, anc the pressure in the fourt=h accumulator 222 is utilized to fomrce the float under the wa . ter. As the fourth two-way valve 238 shuts, the third two-way valve 236 opens, and the pressure in the third accumulator 2220 is utilized to force the float furttmer under the water. Here=fter the third two-way valve 236 sshuts, and the second two-way valwwe 234 opens, and the pre=ssure in the second accumulator 218 is utilized to force the float ev—en further under the wate=r. :

Subsequently, the second two-way valve 234 shuts, ard the flrst two-way valve 232 opens such that the pressumre in the first accumulator 216 is Lased to force the float furt her under the surface of the water— Finally, the first two-way valve 2232 shuts, and the pressure= valve 178 opens.

It will thus be appresciated that at least a portion of the= potential energy releasec as the float 124 moves verticaliyw out of the wave from position 173g to position 174h (cf. th e lower part of Fig. 21) may be umtilized for forcing the float into the water at a wave trough 1.52 in order to increase the powe=r output of the wave power apparatus. Accordingly, the forcing down of a float by in the mariner described above may be regam-ded as a way of utilizing he potential energy released at v=vave crests, which energy would oherwise be lost.

There may be provicied mare than four accumulators 2216, 218, 220 and 222. For example, ; there may be provid ed six, eight, ten, twelve, twenty or even more accumulator—s. :

Fig. 23 generally shows a graphical representation of t he accumulation of energy in N steps, i.e. in N accumulatos-s corresponding to the accumulators 216, 218, 220 and 222 of Fig. 22.

The first axis indicat-es the vertical displacement do 250 of the float in water, anc the second axis indicates the fomce F, 252. The area of the hatchec triangle covering half of the diagram of Fig. 23 Indicates t=he Ideal maximal energy, which Is avaliable. However, in oreder to utilize this energy, the system should comprise an Infinitive nsumber of steps, i.e. an infinite number of accumulators. In eother words, the larger the pressumre difference Is between hwo steps, the larger is the loss of e=nergy for each step. In Fig. 23, thme energy loss Is indicated by hatched triangles 254. Each toriangle Indicates that the float is dllisplaced a vertical distance Ad. The area of each of the ssmall triangles is half height times Hength. Thus, the loss at e=ach step may be determined Eby the following formula: 2

Arran 2 (5 sa) aa - 5

Wherein

Fo Is the excursion force when the float Is forced thme distance do under the wwater,

Ad = d=/N, and

N is thea number of steps.

The total lo: ss of energy i.e. the sum of the small triangles=s, is defined by the following formula: 1(F) (do (%) Fd =— | |e} == || — CN =2"¢ 2 Asc or soc 2 5) (& N 2N

Accordinglyw, the larger the number of step N, the smaller— Is the total loss of energy.

The effect «of the accumulators discussed above in conneaction with Figs. 22 and 23 is shown in Fig. 24, Bn which curve 256 shows the movement of thme float in the wave as a function of time, and curve 258 shows the shape of a'wave as a funsction of time. There is a partial overlap of he curves 256 and 258 at the downstream, |. €. descending, side of a wave. At 260, two-wasay valve 200 shuts (cf. Fig, 22) while pressur—e valve 178 is also shut, and the fioat is loclkeced. At 262, the float moves out of the wave aand delivers energy to the accumulators 216,218,220 and 222. In Fig. 25, curve 2864 shows the actual depression of the floatin the wave.

Claims

1. A wave ppower apparatus comprising at least one arr, the arm being rotationally supported at one end by a shaft and carrying a float at its other end, which is opposite to the supported send, so that a translational movement of the= float caused by a wave results in rotation of the arm around the shaft, the apparatus cormnprising power conversion means for converting power transmitted from the wave to the arms Into electric power, characteris=ed by a hydraulic= lifting system for lifting the float out of the eocean and for locking the float In an upper position above the ocean surface.

2. A wave ' power apparatus according to claim 1, wherein the float is pivotally joined to the arm.

3. A wave power apparatus according to claim 1 or 2, ccomprising a plurality of arms, each arm being supported by at least two bearings which aree arranged along a common centre axis, which is coincident with an axis of rotation of the am, the bearings being offset from the centre axis, so as to counteract radial and axial forces.

4. A wave power apparatus according to claim 3, whereeln the bearings are pre-stressed In an axial direc®ion.

5. Awave power apparatus according to claim 3 or 4, waherein each of the bearings comprises an Inner a nd an outer ring or cylinder, the Inner ring b-eing secured to a rotational shaft of the arm, amnd the outer ring being secured to a fixed sLapport, the bearing further comprising a flexible rnaterial between the Inner and the outer rineg.

6. A wave power apparatus according to claim 5, wher—ein the flexible material comprises at least one acavity or perforation.

7. A wave power apparatus according to claim 5 or 6, wherein the flexible material comprises at least ore spring member, such as a flat spring.

8. A wave: power apparatus according to any of the preeceding claims, wherein the at least one arm comprises a plurality of arms which are arranmged in a row such that a wave passing the row off arms causes the arms to successively pivotz around the shaft, the arms being arranged .at mutual distances, so that at all times at last two of the arms simultaneously deliver a ppower contribute to the power conversion me=ans, the power conversion means

YRWVO 2005/038248 PCT/EDK2004/000705 cod mprising a hydraulic actuator associated with each arm, the hydraulic actuators feeding a hydraulic medium Into at least one hydraulic motor via common hydraullc ccanduits.

9. A wave power apparatus according to claim 8, wherein the row of arms Iss oriented such with respect to the wave heading that the row forms an angle of within +/- 600 with respect to the heading.

1 ©. A wave power apparatus according to claim 8 or 9, wherein each of the arms irtermittently transmits power to the power conversion means when a wave passes the float of the arm, the arms and floats being arranged with such mutual distances that, at all times, amt least two arms and floats simultaneously deliver a power contribute to tive power conversion means.

M_1. A wave power apparatus according to any of the preceding claims, whe=rein buoyancy of he float is at least 10 times its dry weight,

12. A wave power apparatus according to any of the preceding claims, whearein the diameter oof the float is at least 5 times its height.

1.3. A wave power apparatus according to any of the preceding claims, whe=rein the plurality «Of arms comprises at least five arms per wavelength of waves.

14. A wave power apparatus according to any of the preceding claims, wherein the plurality of arms comprises at least five arms spanning over a total length of 50 —- =200 m.

15. A wave power apparatus according to any of the preceding claims, wh-ereln the arms and the floats are made from a material which has a density of at most 1000 lexg/m3.

16. A wave power apparatus according to any of the preceding claims, whi erein the power conversion means comprises a hydraulic driving system with at least one “hydraulically driven motor.

17. A wave power apparatus according to claim 16, wherein each arm Is cconnected to the hydraulic driving system by means of at least one actuator which causes aa hydraulic medium of the hydraulic driving system to be displaced into one or more mutual motors, the actuators being arranged to displace the hydraulic medium to the motor(es) via common hydraulic conduits.

18. A wave power apparatus according to claim 17 _, wherein the at least one actuator of each arm comprises a double-acting cylinder.

19. A wave power apparatus according to claim 18 , wherein the double-acting cylinder forms part of the hydraulic lifting system, so that the cyll nder is controllable to lift the float out of the ocean.

20. A wave power apparatus according to claim 18- or 19, wherein the hydraulic driving system comprises at least one hydraulic accumulator for intermittently storing energy in the hydraulic driving system, and wherein the hydraullic driving system is controllable to release the energy stored in the accumulator, when a float is passed by a wave trough, so as to force the float carried by the arm Into the wave.

21. A wave power apparatus according to claim 17 and 20, wherein the hydraulic medium Is fed to the hydraulic accumulator system via the common hydraulic conduits.

22. A wave power apparatus according to any of ¢ laims 18-21, wherein each cylinder is provided with a sensor for determining a position &nd/or rate of movement of the cylinder’s piston, the sensor being arranged to transmit a sicgnal to a control unit of the cylinders and associated valves, so that the transmission of enemgy from the individual cylinders to the remaining parts of the hydraulic driving system is individually controllable in response to the signal representing the individual cylinder's piston-“s position and/or rate of movement.

23. A wave power apparatus according to any of t"he preceding claims, wherein the shaft and the power conversion means are supported by a s upporting structure which Is anchored to the sea floor by means of a suction anchor.

24. A wave power apparatus according to claim 233, wherein the supporting structure is anchored to the sea floor by means of a suction asnchor and/or a gravitational support.

25. A power apparatus according to claim 23 or 24, wherein the supporting structure comprises a truss structure, and wherein the suction anchor is arranged in a first nodal point= of the truss structure.

26. A wave power apparatus according to claim 255, wherein the supporting structure comprises a truss structure, and wherein the at le:ast one arm Is supported by the truss structure In a second nodal point thereof.

27. A wave power apparatus according to claim 26, wherein said second nodal point is arrancyed at a summit of a triangular subsstructure of the truss structure, and vavherein the triang ular substructure defines two vertices at the sea floor, with an anchor in each of the cornem-s,

28. A wave power apparatus according to claim 27, wherein the truss structures comprises a polygeonal substructure, preferably a rectangular substructure, arranged abovea the triangular substmructure,

29. A= wave power apparatus according to any of claims 23-28, wherein the stapporting struct=ure comprises a ballast for providineg a downward force on the supportinegg structure, the ballasst being arranged above sea level.

30. A wave power apparatus according ta claim 29, wherein the ballast comprises at least one be allast tank or ballast container.